1. Field of the Invention
The present invention relates to a recording and reproducing method for a dye-based recordable DVD medium on which information can be recorded and from which such information can be reproduced by irradiating it with a light beam to cause its recording layer to undergo optical changes such as transmittance change and reflectivity change, and to an apparatus for the recording and reproducing method.
2. Description of the Related Art
At present development has been underway for recordable digital versatile discs (DVD±R) that can offer enhanced recording speed as large-capacity optical discs. Main technologies for increasing recording capacity involves, for example, development of recording materials that can reduce the length of recording pits, and technical development that can reduce the wavelength of semiconductor laser beams so that image compression formatting technologies as typified by MPEG2 can be adopted for the readout of recording pits.
As semiconductor lasers of red wavelength, only AlGaInP laser diodes of 670 nm wavelength have been commercially utilized in, for example, barcode readers and instrumentation units. Red lasers, however, are now widely used in the optical storage market along with the progression in high-density optical discs. For example, DVD drives are standardized using laser diodes of two different wavelengths for their beam source: 635 nm and 650 nm. Meanwhile, DVD-ROM (Read Only Memory Digital Versatile Disc) drives using beam sources of up to 650 nm wavelength are now commercially available.
In dye-based recordable DVD media in which pits or marks are typically formed with heat mode, the pulse width and recording power of recording pulse of a laser beam applied upon recording are optimized at a particular recording speed, and the status of marks and/or spaces to be formed vary in the other recording linear velocity range, leading to the following problems: insufficient thermal capacity of heating pulses required to form marks, variations in the average mark length due to differences in heat temperatures required before reaching an optimal decomposition temperature, and non-uniform mark widths due to the difference in the duty ratio of an optimal heating pulse, which in turn leads to the generation of thin marks or thick marks according to mark lengths. For these reasons, jitter characteristics undesirably become deteriorated.
In addition, although Japanese Patent Application Laid-Open (JP-A) No. 2004-303400 and other several literatures disclose that high-quality recording can be realized at a recording linear velocity of 42 m/s or less, recording at a recording linear velocity of greater than 42 m/s cannot provide sufficient recording quality depending on the type of recording media.
With respect to physical formats of DVD media, DVD-R media are standardized with a format in which land portions (or so-called land prepits) are partially cut. When this format is applied, prepit information such as prepit addresses cannot be properly reproduced if the land prepit signal (LPPb) is less than 0.16; whereas if the land prepit signal is greater than 0.32, LPP signals themselves behave as noise components in data areas, thus resulting in the frequent occurrence of data errors. Accordingly, there is a disadvantage that the land cut width should be adjusted according to recording material using a stamper, so that the LPPb falls within a range of 0.16 to 0.32.
There are a number of known optical recording media using dyes, and examples thereof include those using as recording material polymethine dyes or combination of polymethine dyes and optical stabilizers; those having a layer made of tetraazaporphyrin (porphyrazin) dye or a combination of cyanine dyes and azometalchelate dyes (salt forming dye), and a reflective layer; those using as recording material a combination of formazane (metal chelate) dye and the other dyes; and those using as recording material a combination of dipyromethene (metal chelate) dye and the other dyes. Furthermore, there are a number of known optical recording media in which dyes are used as recording material for multi-pulse recording.
However, there is no technology that allows single pulse recording to be performed on dye-based recordable DVD media while optimizing the recording waveform for high linear velocity recording and optimizing recording and reproducing operations.